Art of distillation



Patented Oct. 8, 1929 yUNITED STATES EUGENE H. LBLIE, OFANN ABBOB, MICHIGAN .ABT OF DISTILLATION Application led April 19,

This invention relates to art of distillation; and it relates more particularly to a process of and apparatus for effecting distillation of liquid mixtures, wherein the liquid mixture to be distilled is heated in a suitable still or vaporizer, the resultant vapors are fractionated in any appropriate form of fractionating apparatus, a portion of the vapors from thel fractionating apparatus are condensed and refluxed thereto, and the remaining vapors are then condensed tothe final product of distillation, the transfer of heat from the saturated or superheated vapors undergoing p reflux condensation in the refiux cooler or partial condenser being accuratel and exactvly controlled in a novel and a vantageous manner.

In effecting more or less complete separa- ,I tion of a more volatile from a less volatile 2o component of a liquid mixture, it is common practice to heat theliquid in a still or vaporizer and to pass the resultant vapors through fractionating apparatus of suitable type, such as a column, dephlegmator, or other appropriate apparatus whereby the composition of the vapors is changed in such manner that they become progressively richer in the more volatile component. It is essential that a portion of the vapor be condensed and returned to the top of the column, or other form of fractionating system employed, in order that the fractionating system may function properly, and this is true for both batch and continuous distillation. The quantity of liquid that necessarily must be so returned per unit weight of the nal product or products obtained is mathematically related to the composition of the product or products, the composition and Weight of the vapor entering the column or fractionator, and also, in continuous distillation, to the Weights and compositions'of the feed entering, and of the liquid residue leaving, the system. These relationships are conditioned by the inherent thermodynamic properties ofthe substances com/posin g the liquid solution or mixture that is being distilled. Because of the definiteness of the relationships just mentioned, it is ofgreat importance, if the process is to be most efficient, that the weight of reflux condensate 1923. Serial No.`688,296.

be controlled with as much precision as is reasonably possible in commercial practice. The importance of this factor does not a pear to haveV been fully appreciated heretofdre, nor has provision been made whereby such control can be attained with anything like ,the precision necessary'for most satisfactory and dependable operation of a distillation system. It is accordingly a principal object of the present invention to provide a method and an apparatus whereby control of the heat transfer in the refiux operation, and hence the quantity of the reflux condensate returned to the. fractionating system, may be controlled with precision and certainty.

In the practice of the present invention, the cooling medium employed in the refiux cooler or partial condenser is one that boils, under the conditions of operation, at atemperature below the boiling point of the liquid in equilibrium with the vaporsvexiting from the reflux device; andthe conditions of operation are such that such lower-boiling cooling medium is maintained constantly boiling. In other words, the cooling medium is continuously converted into vapor at the particular pressure prevailing, and in undergoing this change of state each unit weight of the cooling liquid that is vaporized absorbs from the vapors conducted into the reflux unit a detinite quantity of heat, that is, the latent heat of vaporization of the substance, solution, or mixture, used as the cooling medium. Suitable provision is made to guard against change in composition of the cooling medium; and its effective action as a heat-absorbent may be exactly adjusted in accordance with requirement by providing suitable means for varying either the conditions under which the cooling medium boils or the heat-transferring relation between it and the vapors of the distilled liquid. One way of effecting such adjustment is to vary the quantity of the cooling medium in contact With the heat-transferring surface of the reflux unit as may be necessary to obtain the exact degree of heat transference desired. Another method is to vary the pressure upon the coolin medium and hence-the temperature at w ich it boils.

The underlying principles of the invention can bel further explained to' advantage by way of a concrete example illustrating one practical embodiment of the process and of apparatus suitable for carr ing it into effect. Such an illustrative embo iment of apparatus isshown in the accompanying drawing which illustrates more or less diagrammati-- charge being automatically. governed by the float-controlled valve 14, the particular system here illustrated being adapted for continuous distillation. Vapors leaving the fractionating column'through ipe 15 enter 'the redux cooler or partial con enser 16, passing upwards through tubes 17 which are surrounded by a heat-absorbing liquid medium 18 of the character hereinabove mentioned. A valved pipe 19 permits introduction of said cooling medium into the space surrounding the pipes 17, while valved pipe 2O provides for withdrawing said medium When it is desired to adjust the level ofthe medium 18, the area of the tubes wetted by said medium being thus altered and the cooling effect of such medium thereby adj usted. Vapors evolved in the boiling of the cooling medium 18 are totall condensed and returned to the body'of vsai liquid in the reflux unit. This is accomthe vapor of the cooling medium 18 in the redux cooler 16 to be regulated independently of the pressure of the vapor of such cooling medium in the condenser 22. A non-return valve 32 is arranged in the condensate return pipe 23 and the pipe 23 is made high enough to provide a hydrostatic head sudicient to overcome any desired excess in vapor pressure in the cooler 16 overthat in the condenser 22. Y

Such predeterminable portion of the distillation vapors entering the redux unit 16 through pipe 15, as is condensed by the cooling action of the boiling medium 18, is reduxed to the top section of the distilling C01-, umn 11 through pipe 24. Vapors escaping condensation in redux 16 exit through pipe 25 and enter condenser 26, being condensed therein b 1 the cooling ede'ct of the cooling medium owing through pipes 27, and the resultant condensate, which is the final product, being discharged through Valved pipe 28. The condenser is provided with the usual indow and outdow pipes 29 and 30 for cooling medium. A i l v It is to be understood that in carrying out the rocess of the invention in the above descri d, apparatus, the amount of cooling medium 18 in the redux 16 or the pressure thereon, the rate of distillation, and any other necessary conditions of operation, are so adjusted that said cooling medium 18 boils continuously, thus abstractino' from the `hot distillation vapors a deiinitelx .predeterminable quantity of heat corresponding to the weight ofvapor formed from, and to the latent heat of, vaporization of kthe liquid cooling medium at the pressure prevaihng .in the cooling space of the redux; This ensures the return of an exactly controllable -weight of redux condensate to the top of the column 11 and accordingly enables the whole distilling operation to be controlled with precision and certainty.

'Changing the level of the cooling medium 18 in the redux is to be understood as only typical of various expedients that may be used to edect control and fine adjustment of the quantity of heat transferred in the reflux unit. Such adjustment or control may be edected otherwise as above pointed ont as, for example, by varying the pressure on the cooling medium by adjusting the pressure reducing valve 31. Orl the mean temperature diderence between the distillation vapors andthe cooling medium can be changed by using liquids of diderent boiling points as cooling media. The greater this temperature diderence, the larger the'quantity of heat transferred to the cooling medium from the vapor. It is also feasible to use cooling mixtures of two or more different liquids in various proportions, thus making it possible to give any desired or required value to the mean temperature did'erenc'e. .ifi-

From the standpoint of economy in installation and operation, it is usually@v desirable to employ a cooling medium whofsiboiling point is very much lowervthan that of the liquid in equilibrium with the vapors exiting-from the redux unit, because under these circumstances the transfer of heat is very rapid and consequently a comparatively small and inexpensive redux unit can be used. l

Once the desired conditions are established, they are automatically maintained. The value of this certainty of control is obviously of great importance in the operation of apparatus for continuous distillation or fractionation. Y

- In batch distillation the situation is somewhat diderent. As the distillation proceeds, the weight of the liquid necessarily returned to the top of the column or fractionator changes with the change in composition of the the vapor entering the fractionatin system.

. ing same from the fractionating liquid in the still, or

Accurate control o'f the heat-trans er in the reflux condenser is necessary, but theweight of reflux condensate must increase progressively. The most convenient way of effecting such control in accordance with the present invention, while providing for the progressive increase in Weight of reflux condensate,

' is to utilize suitable means for automatically controlling the level of the cooling medium 18, or of progressively changing the total pressure on, and hence the boiling point of, the said li uid ,18. The first method controls the area o the heat transferring surface, and\ the second the mean temperature difference between the distillation vapor and the cooling medium. Automatic means may also be provided for varying the pressure on the cooling medium as a function of the composition of the liquid in the still 10 or the vapor coming therefrom. Although automatic control is most convenient in practice for attaining the desired progressive increase in weight of reflux condensate, the necessary control can be effected by a still attendant who adjusts the apparatus from time to time in accordance with observations.

It is to be understood that, for the purposes of this invention, the reflux cooler or partial condenser 16, functions substantially only as heat-transferring a paratus, and that 1t is not intended to e ect therein substantial change in the composition ofthe vapors eitersystem. The function of said reflux 16 is t erefore not to be confounded with that of fractionating apparatus, whether of the dephlegmator or fractional condenser ty e.

While certain embo iments of the novel process and apparatus have been hereinabove described b Way of explanatory example for the sake o clearly disclosing the principles of the invention, it is to be understood that the invention is not restricted to said embodiments and that the scope of the invention is indicated in the appended claims.

1. In the art of distillation, the rocess which comprises vaporizing a liqui to be distilled, treatingthe vapors in a fraction ator, subjecting vapors leaving said fractionator to the action of a reflux cooler to partially condense the same for return to said fractionator, while controlling the heat exchange in said reflux cooler by employment therein of a liquid cooling medium that boils under the conditions of operation thereby 'enabling the return 'of an exactly predeterininable weight of said partial condensate to the fractionating system, and conducting away and condensing residual vapors from said reflux cooler.

2. In the art of distillation, the process which comprises vaporizing a liquid to be with the composition of distilled and subjectingx tionation, abstracting iluxin the vapors to fraceat from the vapors resulting from fractionation by bringing such resultant vapors into heat-transferring relation with a cooling liquid of lower boiling point than the liquid in equilibrium with "the vapors exiting from the yheat-transferringmean's and thus partially condensing f said vapors, the conditions being so controlled that such lower boiling liquid is maintained boiling thereby enabling the y.return of'an exactly predeterminable weight of said partial condensate to the fractionating system, re-

tionatlng system, and condensing the residual vapors to obtaina desired distillation product.

3. In thefart of distillation, the process which comprises vaporizing the liquid to be distilled, fractionating the vapors, partially condensing vapors surviving such fractionation by the cooling action of a liquid medium of lower boiling point than that of the liquid in equilibrium with said partial condensate under conditions such that said'medium continually boils thereby enabling' the return of an exactl predeterminableweight of the said resultant'condensate to the fracpartial Acon ensate to the fractionating system, refluxing said partial condensate to said fractionating apparatus, and separately condensing the vapors escaping the partial condensation.

4.-. In the lart of distillation, the process which comprises vaporizing the liquid to be distilled, fractionatmg the vapors, partially condensing the fractionatedva ors in a reiux cooler by the action of a liqui cooling medium that is maintained boiling at a temperal ture below the boiling point of the liquid in refluxl cooler.

6. The process as defined in claim 4, wherein such further control of the amount of reflux condensate is effected by varying the pressure upon' the boiling cooling medium in the reflux cooler.

7. Distillation apparatus comprising the combination, with a vaporizing. and fractionating system, of a reflux cooler connected thereto and into which vapors pass from said system, and a condensing system into which vapors pass from said cooler, said cooler.

' being provided with separated spaces for distillation-vapors and coolin Bruid, respectively, means being aisoprovi ed to condense vapors of the coolin uid'and return the condensate to the coo ing Huid space of said cooler.

8. Distillatio-n apparatus as dened in claim 7, further characterized by the provision of means for adjusting the kcooling action of said reflux cooler.,

9.Disti11ation apparatus as defined in claim 7, further characterized by the provision of means for varying the effective cooling surface area of said reiiux cooler to ad'ust vits cooling action.

n testimony whereof I hereunto aix my signature.

EUGENE H. LESLIE. 

